Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 18 Nov 2011 10:41:27 -0600

Hi Kevin,

On 2011-11-17 you wrote:
> I'm using a stringout record and I noticed that it only writes the
> string to the PV specified in the OUT field when the string changes.  I
> was hoping to change this.  I took a look at the stringout fields and
> noticed two fields that are set to "On Change":

Looking at the source code the record does call the device support's write 
routine every time it processes.  Your dbpr output which I snipped showed that 
you're using Soft Channel device support but the OUT field is empty, so it's 
not actually writing the string value anywhere.  However it looks like you 
don't really need it to, and you're really asking about it posting channel 
access monitors instead...

> Unfortunately I can't find documentation for the APST and MPST fields.
> I've searched tech-talk, as well as this page (and fields common to all
> & many record types):
> 
> http://www.aps.anl.gov/epics/wiki/index.php/RRM_3-14_String_Output
> 
> Is there a record documentation location I've missed?  What do the APST
> and MPST fields do?

They control when the record posts CA monitors (MPST => value monitors, APST 
=> archive monitors) on the VAL field.  For your needs I think you just want 
to set the MPST field to "Every time" (or whatever the choice string actually 
is).

The APST and MPST fields exist in the aai, aao, stringin and waveform records 
too, but it looks like you're right that no documentation exists to describe 
them.  I'm copying this reply to tech-talk in the hope that someone who has a 
wiki account will be willing to add something about them to the 
http://www.aps.anl.gov/epics/wiki/index.php/RRM_3-14_Common "Fields common to 
many record types" and to the pages for those 5 record types.

- Andrew
-- 
Optimization is the process of taking something that works and
replacing it with something that almost works, but costs less.
-- Roger Needham

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System